Method for clarifying liquids

ABSTRACT

An aqueous liquid containing suspended solids is clarified by a procedure in which attapulgite clay (preferably a concentrate of the attapulgite mineral content of such clay) is initially dispersed in the aqueous suspension. Before flocs form, there is incorporated an organic polymeric polyelectrolyte which interacts in situ with the deflocculated clay material to form flocs which occlude the matter that was originally suspended in the water. The clay material is preferably subjected to intensive mechanical work in the presence of water before it is added to the liquid to be clarified.

United States Patent [72] Inventor John R. Fanselow Kalamazoo, Mich.[21] Appl. No. 838,335 [22] Filed July 1, 1969 [45] Patented Nov. 2,1971 i [73] Assignee Engelhard Minerals & Chemicals CorporationWoodbridge, NJ.

[54] METHOD FOR CLARIFYING LIQUIDS 1 Claim, No Drawings [52] U.S. Cl210/47, 210/53 [51] lnt.Cl B0ld 21/01 [50] Field of Search 210/51-54[56] References Cited UNITED STATES PATENTS 2,795,545 6/1957 Gluesenkamp210/54 X 2,981,630 4/1961 Rowland 210/54 X 3,066,095 1 H1962 Hronas210/53 3,142,638 7/1964 Blaisdell et al.. 210/53 X 3,342,742 9/1967Cocks 210/52 X Primary Examiner-Reuben Friedman AssistantExaminer-Thomas G. Wyse Attorneys-Melvin C. Flint and lnez L. MoselleABSTRACT: An aqueous liquid containing suspended solids is clarified bya procedure in which attapulgite clay (preferably a concentrate of theattapulgite mineral content of such clay) is initially dispersed in theaqueous suspension. Before flocs form, there is incorporated an organicpolymeric polyelectrolyte which interacts in situ with the deflocculatedclay material to form flocs which occlude the matter that was originallysuspended in the water. The clay material is preferably subjected tointensive mechanical work in the presence of water before it is added tothe liquid to be clarified.

Mmuon son CLARIFYING mourns BACKGROUND OF THE INVENTION US. Pat. No.3,128,249 to David J. Pye et al. describes a method for clarifying watercontaining finely divided suspended solids. Wyoming bentonite or otherclay composed predominantly of a mineral having the montmorillonitestructure and a small amount of an acrylamide polymer are introducedinto the water. Flocs comprising the bentonite (montmorillonite) clayand suspended solids form as a result. The flocs settle from the waterand are separated by conventional treatments such as filtration orsedimentation.

A similar method is described in US. Pat. No. 3,066,095 to John J.Hronas. This method features the treatmentof water containing suspendedmaterial with an inorganic coagulant such as alum, preferably beforeadding colloidal clay and any one of several types of organicpolyelectrolytes. This patent also emphasizes the desirability of usinga swelling bentonitic clay. US. Pat. Nos. 3,130,167 and 3,276,998, bothto Jerome Green, describe similar treatments which utilize bentonite orsaponite as the coagulating clay. According to the teachings of theprior art, exemplified by the patents mentioned above, the order ofaddition of the clay and polyelectrolyte is not critical. Generally, thesubstantially simultaneous addition of clay and polyelectrolyte isadvocated.

Saponite clay and the so-called bentonite" are members of the family ofmontmorillonite clays. Such clays are described by Ralph E. Grim in histext CLAY MINERALOGY, Mc- Graw-Hill Book Company, Inc. (I953) at pages58 and I18. As described in the Grim text, the montmorillonite clays arecharacterized by a platy, layered structure.

In describing the function of the montmorillonitic clays as coagulatingagents, the patents frequently refer to the formation of hydrous flocs"as a result of the use of the clay in conjunction with organicpolyelectrolytes. The clay is more specifically described as a weightingagent" in an article by Ralph L. Carr, Jr. POLYELECTROLYTE COAGULANTAIDS," W. & S. W.-Reference Number 1967) page R-66-7 2. In an articleappearing in CHEMICAL & ENGINEERING NEWS, Jan. 15, I968, page 46, thebentonite clay is said to make the flocs heavier.

THE INVENTION An object of this invention is to provide an improvedmethod for clarifying aqueous liquids with a combination of clay andorganic polyelectrolyte, the method featuring the use of mineralmaterial which is generally more effective or efficient than the samequantity of a montmorillonite clay would be.

I have discovered that the rate of floc formation, particle size of theflocs, rate of settling and the clarity of the supematant liquid aresignificantly affected by the mineral species that is employed with anorganic polyelectrolyte to clarify an aqueous liquid. I have found thata given quantity of a specific nonswelling clay mineral which is not amember of the montmorillonite family generally produces significantlybetter results when employed in a manner described hereinafter than maybe realized with members of the montmorillonite clay group.

Briefly stated, in accordance with this invention, an aqueous liquidcontaining suspended solids is clarified by dispersing therein adeflocculated aqueous dispersion of acicularhydrated attapulgitecrystals, which crystals have never been thoroughly dried. Preferably,the aqueous clay dispersion is one that has been subjected to high-shearagitation. Before flocs form, there is incorporated an organicpolyelectrolyte which reacts in situ with the originally dispersedacicular attapulgite crystals to form rapidly settling flocs whichentrap the solids suspended in the liquid. The flocs are separated fromthe clarified supernatant by conventional means.

From this brief description of the invention it is apparent that anessential feature resides in the use of acicular attapulgite crystals.Ultrafine grinding which breaks down the individual crystals impairs theeffectiveness of the mineral. Extensive drying also has an adverseeffect.

Another feature is that the mineral is preferably incorporated in thesuspension to be clarified in the form of an aqueous dispersion whichhas previously been subjected to intensive mechanical agitation. Unlikehigh-energy dry grinding of the mineral, this agitation has a verybeneficial effect on the ability of the clay mineral to react with theorganic polymer and form flocs.

Still another feature of the method of the present invention is that theaqueous dispersion of the clay and the organic polyelectrolyte are addedseparately to the suspension to be clarified, the organicpolyelectrolyte being incorporated before fioc formation takes place.

In accordance with a preferred embodiment of the invention, themechanically worked (sheared) dispersion of attapulgite or attapulgiteclay contains a small amount of an inorganic polyanionic sodium salt,preferably a sodium-condensed phosphate, as a defiocculating agent.

When an organic polyelectrolyte reacts with dispersed colloidalattapulgite crystals to form flocs, in accordance with my invention, theflocs are generally more voluminous, fonn more rapidly and settle morequickly than when any one of alum, organic polyelectrolyte or the claymaterial is used alone or when a swelling bentonite is substituted forthe attapulgite or attapulgite clay. The conjoint use of attapulgite orattapulgite clay and organic polyelectrolyte results in more rapid andvoluminous floc formation and in more effective clarification of thesuspended particles since these particles are entrapped in the flocs.Thus, by practice of the principles of this invention clarification ismore efficient and the capacity of a treatment plant may be increased.When economic or other considerations do not dictate improved capacityin a clarification plant, the principles of this invention may be usedto realize an increase in the quantity of suspended solids that isremoved from an aqueous suspension.

DETAILED DESCRIPTION The invention is applicable to the clarification ofwater containing suspended minerals such as clay (e.g., surface waters)and insoluble carbonates or hydroxides (e.g. artesian waters). Animportant application is the removal of colloidally dispersed organiccoloring matter such as the impurities which are present in swamp andbog waters. The treatment of waters containing colloidally dispersedcoloring matter differs principally from the other treatments in thatthe removal or organic coloring matter requires pH control to a valuebelow 7.0.Alum may be used to control the pH. Suspensions of inorganicsolids may usually be clarified by the clay and organic polymer over awide range of pH values, e.g., a pH within the range of about 3 to 10.

There is a correlation between the quantities of attapulgite and polymeradded and the rate at which flocs form and the size and settling rate ofthe flocs. Increase in the concentrations of either one or both of thesereagents generally increases the rate of fioc formation and alsoincreases the particle size and settling rate of the flocs.

Generally speaking, the attapulgite clay or attapulgite mineral isemployed at a concentration within the range of 5 to p.p.m. (expressedon the moisture-free weight of the clay material). Especially goodresults have been obtained when using the clay or mineral at aconcentration within the range of 10 to S0 p.p.m.

The relative proportions of polymeric polyelectrolyte and clay ormineral vary with the concentration of clay or clay mineral, the polymerspecies and the nature of the liquid to be clarified. Economicconsiderations are also of significance since the organicpolyelectrolytes are generally substantially more expensive thanattapulgite clay or an attapulgite mineral concentrate from such clay.Generally the polymeric polyelectrolyte is employed at a concentrationwithin the range of 0.01 to 2 p.p.m. When employing clay material atpreferred concentrations within the range of 20 to 50 p.p.m., excellentresults were realized with at least 0.05 ppm. polyanionic polymer. Atclay concentrations within the range of 5 to 20 ppm. polymerconcentrations of at least 0.2 p.p.m. produced satisfactory results.

The organic polyelectrolytes employed in carrying out this invention aresynthetic water-soluble or water-dispersible high-molecular-weightorganic polymers which form electrically charged organic ionsdistributed along the polymer chain when the polyelectrolyte isincorporated in water. Anionic polyelectrolytes, polyelectrolytescontaining both anionic and nonionic groups and cationicpolyelectrolytes may be used.

Anionic polymers contain a multiplicity of carboxylic groups distributedon the molecule. Examples are: acrylamide polymers, polyacrylic acid,sodium polyacrylate, sodium polymethacrylate, maleic anhydride-vinylacetate, polyvinylmethylether-maleic anhydride, methacrylicacid-methacrylamide, acrylic acid-styrene copolymer, polyvinyl acetate,sodium salt of styrene maleic anhydride, polyvinyl pyrolidone anditaconic acid-vinyl acetate. The acrylamide polymers encompasshomopolymers of acrylamide and copolymers of acrylamide with up to aboutpercent by weight of an aliphatically unsaturated copolymerizablemonomer such as acrylic acid, methacrylic acid, alkyl esters of theaforementioned, methacrylamide, styrene, vinyl acetate, acrylonitrile,methacrylonitrile, vinyl alkyl ether, vinyl chloride, vinylidenechloride. Especially recommended are water-soluble acrylamide polymershaving a low degree of cross-linking between polymer chains such as thepolymers described in U.S. Pat. No. 2,625,529 to Hedrick et al.

Cationic electrolytes are useful in clarifying suspensions of positivelyand negatively charged solids. Members of this class include, forexample, the high molecular weight, water-soluble linear quaternaryammonium polymers described in US. Pat. No. 3,288,770 to Butler andexemplified by homopolymers of diallyldimethyl-ammonium chloridesupplied under the trade name Cat-Floc."

Attapulgite clay includes a mixture of the mineral attapulgitewithsmaller quantities of montmorillonite, calcite, ferruginous matter andquartz. Some properties and characteristics of attapulgite clay and themineral attapulgite are described in the following patents andpublications:

Grim, APPLIED CLAY MINERALOGY," published by McGraw-l-lill Book Company,Inc. (1962) US. Pat. No. 3,080,214 James B. Duke et al.

Raw attapulgite clay as mined may be employed in practicing theinvention after the clay has been mixed with water to form a fluidsuspension'is preferably subjected to high-shear mechanical agitation inthe presence of a deflocculating agent such as sodium silicate or asodium Lcondensedphosphate salt. The claymay be mildly dried before itis incorporated with water and subjected to high-shear agitation. Driedattapulgite clay products, e.g., extruded pelleted products, should bedried at a product temperature below about 300 F. Drying should beinsufficient to reduce the volatile matter of the clay below about l8percent by weight.

The preparation of deflocculated aqueous dispersions of attapulgite clay(Attapulgus fullers earth) is described in US. Pat. No. 3,080,214(supra). When the dispersion is prepared with a deflocculating agent,the raw clay-water suspension that is subjected to high-shear agitationmay have a solids content up to about 28 percent by weight (calculatedon the volatile-free or V.F. clay The terms volatile-free clay weight,"volatile matter" and free moisture" are defined in the Duke ct al.patent. At solids contents above about 28 percent, slips of attapulgiteclay may be too viscous to subject to high-shear agitation. Without adeflocculating agent, fluid suspensions of raw clay may contain up toabout 5 percent clay solids (V.F. basis). It is preferable to removecoarse grit from the clay-water suspension before it is used to clarifywaste liquids. Grit removal may be effected before or after high-shearagitation, preferably before. This may be accomplished by passing thesuspension through screens of suitable dimensions, tag, a 325-mesh Tylerscreen.

High-shear agitation may be provided for example by colloid mills, aWaring Blendor, or by impeller agitators operating at high speed.Generally, high-shear agitation is characterized by the fact that theaqueous suspension increases substantially in temperature during theagitation. The mechanically worked deflocculated suspensions arecharacterized by the fact that the individual attapulgite clay crystalsare separated from each other. The efi'ectiveness of attapulgite clay orattapulgite as a clarifying agent is improved substantially bysubjecting a deflocculated aqueous-dispersion of the mineral material tohigh-shear agitation before the mineral suspension is incorporatd intothe liquid to be clarified.

The preferred clay material is a mechanically worked deflocculatedaqueous dispersion of a concentrate of the mineral attapulgite obtainedby removing at least a substantial proportion of montmorillonite as wellas quartz and other impurities from attapulgite clay. A method forforming a mechanically worked deflocculated aqueous concentrate of themineral attapulgite from attapulgite clay is described in detail in thecopending application of Tom A. CCecil et al., Ser. No. 640,313, nowU.S. Pat. No. 3,477,565. Briefly, the process described in the Cecil etal. application involves mixing raw clay with water and a deflocculatingagent, using sufficient water to form a fluid-concentrated system,subjecting the mixture to high-shear agitation, degritting thedispersion and maintaining the degritted dispersion under quiescentconditions until the mixture fonn a multiplicity of deflocculatedstrata, the strata differing in mineral content. A deflocculatedmontmorillonite-enriched strata and deflocculated attapulgite-enrichedstrata are separated from each other in order to provide the desireddeflocculated aqueous concentrate of the mineral attapulgite. Asproduced by the procedure of the copending Cecil et al. application, thedeflocculated mechanically worked attapulgite slip may contain up toabout 10 percent solids (V.F. basis). Thisslip may be shipped in aqueousform for use in a water clarification plant. Alternativcly, the slip maybe mildly dried by spray drying, for example, to provide a predispersedsolid attapulgite additive. The temperature and duration of dryingshould be carefully controlled to avoid reducing the volatile matter(V.M. of the mineral below about 18 percent. When using the predispersedmicrospheres, the microspheres should be incorporated into water,preferably with additional deflocculating agent, and the mixture tohigh-shear agitation before use in clarifying suspended solids.

Preferably the attapulgite concentrate has the lowest content ofmontmorillonite as possible. I have found, unexpectedly, that themontmorillonite component of attapulgite clay is significantly lesseffective for clarification purposes than the attapulgite component ofsuch clay.

lt has been brought out above that the aqueous suspension of the claymaterial preferably includes a deflocculating agent (dispersant) whichmay be incorporated during processing or subsequent to processing of theclay. Suitable deflocculating agents include sodium silicate, sodiumhexametaphosphate, sodium tripolyphosphate, tetrasodium pyrophosphate,ammonium hydroxide, sodium hydroxide and mixtures thereof. Theproportion of dispersing agent relative to clay or clay mineral varieswith the species of dispersant and is generally within the range ofabout 0.5 to 5 percent of the V.F. weight of the clay material. Thedispersant has a fluidizing agent effect on the clay-water system.Therefore, when a dispersant-effective proportion of a deflocculatingagent is present, the claywater system will have a lower viscosity thanit would in the absence of the dispersant. For example, a 20 percentsolids aqueous suspension of attapulgite clay would be a solid orsemisolid mass in the absence of a strong deflocculating agent. With asuitable deflocculating agent, the suspension would be fluid andamenable to high-shear agitation.

It may desirable to add a supplementary quantity oF deflocculating agentto a predispersed aqueous suspension of the clay material in order toincrease the fluidity of the suspension before the clay is incorporatedwith liquid to be clarified. For example, a small amount of sodiumcondensed phosphate (e.g., 0.5 to 2 percent of the weight of the mineralsolids) may be added to a degritted deflocculated suspension of wholeclay or to a deflocculated aqueous concentrate of the mineralattapulgite obtained by the quiescent settling of said suspension inaccordance with the process described in the copending application ofCecil et al.

in putting the invention into practice, deflocculated aqueous dispersionof the clay material, preferably a mechanically worked dispersion, isincorporated in suitable proportion into the liquid containing suspendedsolids. The termclay material" encompasses attapulgite clay includingother clay minerals normally present in the raw clay as mined as well aspure attapulgite and attapulgite concentrates obtained by removal ofgrit and montmorillonite from whole clay. The clay dispersion should bethoroughly mixed with the liquid to be clarified.

The organic polymer must be incorporated in the liquid to be clarifiedbefore fiocs appear. Preferably the polymer is incorporated as a dilutesuspension or dispersion, e.g., at a concentration within the range ofabout 0.1 to 0.5 percent by weight. The addition of polymer should befollowed by mild agitation in order to uniformlY distribute the polymerin the aqueous system. Generally the clay material should be addedbefore the organic polymer. In some cases it may be possible toincorporate a dispersion of organic polyelectrolyte into the suspensionto be clarified before incorporating the clay dispersion withoutflocculation occuring before the clay dispersion is added. In such acase the organic polyelectrolyte may be incorporated before the clay.Similarly, with some systems it is possible to add a dispersion ofpolymer and a dispersion of clay material concurrently while mixing theliquid suspension. However, the organic polyelectrolyte cannot bepremixed with the clay material before either one is incorporated in theliquid to be clarified because the clay and organic polyelectrolyte willinteract prematurely, thus precluding occlusion of impurities in theflocs.

The liquid containing the clay material and organic polymer ismaintained under quiescent or nonturbulent conditions until flocs formand settle. Conventional techniques such as thickening by decantationand filtration may be used to recover the clarified supernatant.

EXAMPLE I The following tests were carried out to compare theeffectiveness of a combination of organic anionic polyelectrolyte andvarious clay materials in clarifying a turbid aqueous suspension. Thetests permitted a comparison of the rate of floc formation, thecoarseness of flocs and rate of floc settling. These factors weregenerally closely related.

PREPARATION OF CLAY MATERIALS The sample of Attapulgus clay employed inthis example was a degritted clay obtained as follows.

- An undried attapulgite clay crude from a mine near Attapulgus, Ga. wasemployed as the starting material. This crude contained a mixture ofattapulgite, bentonite, with quartz and calcite as gangue minerals. Thecrude at about 50 percent V.M. was placed in a large Waring Blendor andwas mixed with sufficient water to form a slip containing 24 percentsolids (V.F. weight basis). Tetrasodium pyrophosphate was added inamount of 2 percent based on the V.F. clay weight and the Waring Blendorwas operated for 5 minutes at low speed and then for 5 minutes at highspeed. The resulting fluid deflocculated slip was degritted in aTolhurst centrifuge. The degritted slurry of attapulgite clay (17percent solids) was diluted to 3 percent solids (as determined by ahydrometer). This slurry was employed in tests to remove suspendedsolids, as described hereinafter.

The so-called purified" or enriched" attapulgite used in this examplewas recovered by processing a portion of the 17 percent slip ofdegritted Attapulgus clay in accordance with the procedure described inU.S. Pat. No. 3,477,565 to Tom A. Cecil et al. By this technique amontmorillonite enriched fraction was simultaneously recovered as adilute deflocculated aqueous dispersion. The dispersion ofmontmorillonite was also tested in order to identify the constituent ofthe attapulgus clay that was responsible for its effectiveness inclarifying water.

All mineral additives were formed into dilute dispersions by adding 3parts by weight mineral solids (or suspensions containing equivalentmineral solids) to I00 parts by weight of water having dissolved about0.03 parts by weight sodium hexametaphosphate and shearing the mixturein a Waring Blendor at high speed for 3 minutes.

CLARIFICATION The liquid to be clarified was a dilute (40 p.p.m.)suspension of kaolin clay in tap water.

In all tests, a predetermined quantity of the chemically deflocculatedaqueous mineral dispersion was incorporated into the turbid suspensionof kaolin clay. After addition of the mineral dispersion, the suspensionwas agitated until it appeared to be homogeneous. The suspension wasthen incorporated into an aqueous dispersion of polyacrylamide SeparanNPlO) of about 0.1 percent concentration. To provide mild mixing, themixture was gently poured from one beaker to another at total of 10times.

Clarification tests were carried out with mineral concentrations of 2.5,5, i0, 20 and 40 p.p.m. At each of these mineral concentrations, SeparanNP10" was used at one eighth, one fourth, one half, 1 and 2 p.p.m. (At amineral concentration of 2.5 p.p.m., the minimum Separan" concentrationtested was one half p.p.m.) In this manner the mineral andpolyelectrolyte was tested in systems in which the products of theconcentrations (p.p.m.) of the reactants ranged from one fourth to 80.

Floc formations were rated at each product concentration. The mosteffective mineral-polyacrylamide combination was defined as being theone in which the lowest product of the concentrations of mineral andpolyacrylamide gave the best floc rating. Flocculation was rated by aletter using the following designations:

A" Floc became visible in less than 1 minute and settled a distance of 1foot in 4 to 7 minutes.

8" Floc became visible between i to 2 mlnutes and settled 1 foot in 10:3minutes. Clear supernatant.

C Floc became visible in about 5 minutes and settled l foot in [5:5minutes. Clear supernatant.

D" Floc required 30il0 minutes to form and the flocs were of thepinpoint" type, requiring 40 to 60 minutes to settle l foot. Usually aclear or slightly turbid supernatant.

E" Floc required 1 hour or more to form and usually left a turbidsupernatant.

F Flocs formed more slowly than 1?, usually with minimal clarification.

A D floc was considered to be marginally satisfactory for the treatmentof water intended for industrial or domestic consumption.

The formation of 8" or C" floc in a system which was designed to processa given volume of water to provide a floc formation characterized as D"would result in an increase in the capacity of the plant over designcapacity without sacrificing the quality of the treated water. Forexample, a composition producing a 8" floc (about l0-minute settlingtime) would permit a five-fold increase over capacity obtained with a D"floc (about SO-minutes settling time). A C floc with a 15 -minutessettling would increase capacity by a factor of about 3% compared withthe "D floc. Since a C-type floc would represent an increase in plantcapacity without sacrifice in the water clarity, the productconcentrations which resulted in such a rating were also averaged. Thesmaller the value of the average the more effective the clarification.The relative amounts of mineral requlred to effect a given reduction inturbidity are generally approximately inversely proportionate to theactivity ratings.

With the deflocculated, enriched attapulgite fractiomfrom Attapulgusclay, A" flocs were formed with the following combination of reactants:40 p.p.m. mineral and one fourth to 2 p.p.m. Separan; 20 p.p.m. mineraland l to 2 p.p.m. Separan" (i.e., at product concentrations as low as Bflocs were obtained with: 40 p.p.m. attapulgite concentrate andone-eighth to one-half p.p.m. Separan"; and 10 p.p.m. attapulgiteconcentrate and one-half to 2 p.p.m. Serapan." C" flocs were obtainedwith 10 p.p.m. attapulgite concentrate and one-fourth or one-eighthp.p.m. Separan and with 5 p.p.m. attapulgite concentrate and one-half to2 p.p.m. Separan. At lower concentrations D" or 5" flocs were obtained.The average of the product of concentrations of attapulgite and Separan"to form "C flocs (and thus realize improved plant capacity withoutsacrifice in clarity of the water) was found to be 4+. Thus, thisproduct was rated 4+ by a rating system in which the smaller the ratingnumber the more effective the mineral.

Generally, the most effective floc formation and reduction in turbiditywas obtained with a ratio of from 40 to 100 parts by weight ofattapulgite concentrate to 1 part by weight organic polyelectrolyte.Thus, 8 or C flocs were generally obtained at lower productconcentrations than when the ratio of mineral to polymer was appreciablyless than 40 to l.

The degritted Attapulgus clay which contained naturally occuringbentonite in addition to attapulgite was found to be less effective thanthe attapulgite concentrate. In a series of nine tests, the average ofthe reactant concentrations to produce a C floc was 7. (With theattapulgite concentrate the corresponding value was 4+. As with theenriched attapulgite fraction, optimum ratios of mineral to organicpolyelectrolyte were generally within the range of 40 to 100 to l,respectively.

None of the bentonite or montmorillonites was as effective as theAttapulgus clay or attapulgite fraction from such clay.

Results are summarized in table I.

TABLE 1 EFFECT OF MINERALS IN CLARIFYING AQUEOUS SUSPENSIONS WHEN USEDWITH POLYACRYLAMIDE Average of Product of Mineral Cone.

(p.p.m.) Times "Separan" Conc. (p.p.m.) to Produce C"-type FlocAttapulgitc fraction from Attapulgus clay Altapulgus clay 7 "Ben-A-GelNo. l"'

Western bentonite Southern bentonite Montmorillonite fraction fromAttapulgus clay sodium bentonite thickening agents Data in table 1 showthat the Attapulgus clay was more effective than the bestmontmorillonite clays and that the attapulgite fraction of theAttapulgus clay was most effective. Data for the attapulgite andmontmorillonite enriched fractions of Attapulgus clay indicateconclusively that the attapulgite mineral constituent of Attapulgus clayis responsible for the effectiveness of such clay as a clarificationaid.

EXAMPLE ll This example demonstrates the necessity for controlling thedrying of attapulgite and Attapulgus clay when the mineral is employedfor clarification purposes with an organic polyelectrolyte.

A sample of the aqueous concentrate of the mineral attapulgite (exampleI) was carefully spray dried to produce a pRoduct containing more than18 percent volatile matter. The

spray dried product was mixed with water and sodium hexametaphosphate (1percent of the as is" mineral weight). The mixture was then sheared inthe Waring Blendor and employed with a dilute dispersion of SeparanNPIOX," as described in example I, to clarify a portion of the kaolinsuspension. The product had an outstanding rating of 7.

In contrast, a sample of Attapulgus clay commercially used as in makingup drilling mud had a rating of 17. This clay product has been processedby extruding raw Attapulgus clay into pellets, drying to a volatilematter below l8 percent, crushing and screening.

EXAMPLE lll Colloidal grades of Attapulgus clay in powdered form areused industrially to thicken various aqueous liquids. These products areobtained by fluid-energy-grinding colloidal grades of the clay using airor steam as the vehicle in which the particles are suspended while theyare micronized by highenergy particle-to-particle impact. Samples ofsuch powdered colloidal products were tested with Separan NPlO" as inexample I. All rated above 20. The products were therefore substantiallyless effective'than colloidal Attapulgus clay which had not beensubjected to intensive mechanical work when in pulverulent condition.

The fluid energy ground Attapulgus clays were also less effective whenemployed with cationic polyelectrolytes (Magnifloc 521" and Pn'maflocC-7") and a nonionic polyelectrolyte (Magnifloc 900N") than thedegritted Attapulgus clay product used in example I. The fluid energymilled attapulgite clays were also less effective than the spray driedattapulgite concentrate described in example ll.

Thus it has been shown that processed attapulgite clay and the mineralattapulgite were more effective than bentonitic (montmorillonite) claysin clarifying liquids. This result was unexpected in light of the priorart teaching of the desirability of using a swelling clay forclarification purposes since attapulgite is not a swelling clay. Whilenot wishing to be bound to any theory of hypothesis as to the unusualeffectiveness of attapulgite, experience indicates that when the mineralattapulgite is pretreated as described and employed in the prescribedmanner it is significantly more reactive with organic polyelectrolytesthan the layered minerals.

lclaim:

1. In a process for clarifying an aqueous liquid containing inorganicsuspended solids, the steps which comprise:

providing grit-free, hydrated acicular attapulgite crystals which neverhave been dried to a volatile matter content below 18 percent and whichnever have been mechanically ground,

using high-shear agitation, mixing said crystals in water in thepresence of a deflocculating agent selected from the group consisting ofsodium silicate, sodium hexametaphosphate, sodium tripolyphosphate,ammonium hydroxide, sodium hydroxide and mixtures thereof, therebyforming a fluid aqueous dispersion of said attapulgite crystals,

incorporating said aqueous dispersion of hydrated attapulgite crystalswith said liquid-containing suspended solids in amount sufficient toprovide a concentration of said attapulgite crystals which is within therange of 5 to p.p.m.,

forming a dilute aqueous dispersion of high-molecular weight anionicpolyacrylamide,

incorporating said dispersion of polyacrylamide into said mixture ofaqueous liquid-containing suspended solids and previously incorporatedsheared dispersion of attapulgite crystals, using a sufficient Camountof said dispersion of polyacrylamide to provide a polyacrylamideconcentration within the range of 0.0l to 2 p.p.m., the relativeconcentration of polyacrylamide to attapulgite crystals being sufficientto form flocs in the mixture as a result of interactlon therebetween,

allowing the resulting mixture 6 stand until flocs form, said flocscontaining particles originally suspended in the liquid to be clarified,and removing said flocs from the remainder.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,617,551 Dated November 2 7 l John R. Fanselow It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 2 line 48, "or" should read of Column 3 line 49 insert whichafter "suspension"; line 51, "sodiumLcondensed" should read sodiumcondensed Column 4 line 20, "Tom A. CCecil" should read Tom A. Cecilline 27, "form" should read forms line 40, insert a closing parenthesisafter "V.M. line 45 insert subjected after "mixture"; line 71, "0F"should read of Column 5 line 22, "uniformlY" should read uniformly line38, "conditiOns" should read conditions Column 7 line 75, "pRoduct"should read product Column 8 line 4, "Separan NPlOX should read SeparanNPlO line 70, "Camount" should read amount Signed and sealed this 9thday of May 1972.

(SEAL) Attest EDWARD M.F'LETGHER, JR. ROBERT GOTI'SCHALK AttestingOfficer Commissioner of Patents -ORM PO-10 O USCOMMDC 60370-PB9 U SGOVERNMENT PRINTING OFFICE I9! O-Jll-JSI

